"I've been looking forward to this show... so doing this breaks my heart. However, it's important to always put family first."
The singer is putting her Britney: Domination shows in Las Vegas on hold so she can help with her father Jamie's recovery from "life-threatening health issues", a statement on her website said.
Mr Spears underwent emergency surgery two months ago after suffering a ruptured colon, the star's publicist confirmed to Sky News.
In a post on social media, Spears said that "it breaks my heart" to postpone the shows, but that "it's important to always put your family first".
In her full message to fans, she said: "I don't even know where to start with this, because this is so tough for me to say.
"I will not be performing my new show Domination. I've been looking forward to this show and seeing all of you this year, so doing this breaks my heart.
"However, it's important to always put your family first… and that's the decision I had to make.
"A couple of months ago, my father was hospitalized and almost died. We're all so grateful that he came out of it alive, but he still has a long road ahead of him. I had to make the difficult decision to put my full focus and energy on my family at this time.
"I hope you all can understand. More information on ticket refunds is available on britneyspears.com. I appreciate your prayers and support for my family during this time. Thank you, and love you all… always."
Details of Mr Spears' illness were given in a statement, which said: "Two months ago, Mr Jamie Spears became seriously ill and was rushed to Sunrise Hospital in Las Vegas.
"His colon spontaneously ruptured and he was immediately admitted into surgery. Mr Spears spent the next 28 days in the hospital under the care of the amazing doctors, nurses and staff at the hospital, who the Spears family credits with saving his life.
"After a long, complicated post-operative period, he is recuperating at home and gaining strength, and is expected to make a full recovery.
"Ms Spears has been tremendously involved with caring for her family, and as a result of his health issues and ongoing recovery, she is going to take time off."
Ticket refunds for the shows are available, with details on the Britney Spears website.